(defun start-over()
  ;; define *small* and *big* limit.
  (defparameter *small* 1)
  (defparameter *big* 100)
  (guess-my-number))

;; guess my number function.
(defun guess-my-number ()
  (ash (+ *small* *big*) -1))

(defun smaller ()
  (setf *big* (1- (guess-my-number)))
  (guess-my-number))

(defun bigger ()
  (setf *small* (1+ (guess-my-number)))
  (guess-my-number))

(start-over)